PORTLAND, Ore. — Researchers are using underwater microphones to interpret and characterize the calls of blue whales swimming through Southern California’s oceans, revealing new insights into the behavior of these endangered marine mammals, according to new research being presented at the Ocean Sciences Meeting here on Tuesday.

Stretching nearly 30 meters (100 feet) long and weighing up to 172 metric tons (190 short tons), the endangered blue whale is the largest animal known to have existed. Though the exact purpose of blue whale vocalizations remains elusive, researchers think the whales may use calls to maintain distance between one another, facilitate mating or signal the presence of prey, among other purposes.

A blue whale surfaces off the coast of Southern California, showing the attached tag that records its calls and pressure changes during dives. Researchers use these tags to explore behavioral links between diving and song production.Credit: Ana Širović.

To better understand these vocalizations, scientists recorded and analyzed more than 4,500 sounds from blue whales tagged with underwater microphones and pressure sensors in and around Southern California’s Channel Islands between 2002 and 2016.

The new research compared three types of calling behavior with different diving patterns to uncover behavioral links.

In this recording, you’ll hear two different calls of blue whale swimming off the Southern California coast, sped up three times to bring the sound into a human hearing register. Researchers aren’t yet certain what these sounds mean, but comparing the calls with whale diving behavior can help elucidate their purpose.Credit: Ana Širović.

The researchers found some variability in the times and under what conditions whales call or sing. The vocalizations varied depending on the whale’s sex and the dive’s purpose – behaviors with some similarities to other animals, according to Ana Širović, an oceanographer at the Scripps Institution of Oceanography in La Jolla, California, who will present the new findings Tuesday at the 2018 Ocean Sciences Meeting, co-sponsored by the Association for the Sciences of Limnology and Oceanography, The Oceanography Society and the American Geophysical Union.

“Understanding the context under which blue whales make calls is a critical step in developing non-invasive, non-lethal acoustic methods to study population trends and recovery status of this endangered species,” Širović said. “And as a species on top of the food web, understanding their status and contribution to the ecosystem is important for understanding the status of the ecosystem as a whole.”

The researchers found male whales were chattier at night, when it seemed the animals weren’t feeding. Males produce more calls than their female counterparts, Širović said, indicating some of the calls may aid in reproduction.

The researchers noticed great variability in the male whales’ use of single sounds, as opposed to songs composed of multiple sounds strung together. Other researchers have suggested these single calls could help maintain pair-bonding when males and females meet while foraging. Male bonobo chimpanzees employ a similar strategy, calling to nearby females when food is present, which boosts their chances of mating.

The researchers found dive behavior varies with the seasons, when whales spent more time in shallow waters during late summer and early fall. This may mean whales are hunting for more surface-dwelling prey at those times or traveling, according to the researchers.

The rate at which calls are produced varied within the time of day as well, where song production was highest at dusk and lower during the day. This could be because the whales time their singing for periods when prey is less densely aggregated, though the researchers did not measure prey abundance. A similar, energy-conserving behavior has been observed in European robins and nightingales, who adjust their singing in line with their energy reserves.

A shorter, less far-traveling call past researchers had associated only with foraging behavior seemed to be more socially complex than previously thought. Both males and females used this call during non-feeding dives, leading Širović and her colleagues to suggest it may serve as a close-range call to communicate only with nearby whales.

The research represents the most extensive analysis into the behavioral context of blue whale calling in the region, according to Širović.

2. Today’s press conferences

The AGU press office has planned a number of press conferences highlighting newsworthy research being presented at the Ocean Sciences Meeting. A list of today’s press conferences is below and can be found on the Press Conferences tab in the Ocean Sciences Meeting Media Center.

Pharmaceuticals, microplastics and their byproducts are finding their way into the bodies of Pacific razor clams, Pacific oysters and even showing up in the reproductive tissues of remote seabirds. These emerging contaminants are causing a range of real, potential and unknown biochemical effects on animals and their food webs. In this briefing, researchers will present new results on plastics and pharmaceuticals in coastal marine environments and a review of emerging contaminants in the coastal ocean.

Meteotsunamis: An overlooked hazard for the Great Lakes and beyond
Monday, 12 February
11:00 a.m. PST

You’ve heard of tsunamis – giant oceanic waves triggered primarily by earthquakes that can roll ashore, causing loss of life and disaster. But have you heard of meteotsunamis? These are large waves scientists are just beginning to better understand. They are known to occur in the Great Lakes, the Gulf of Mexico, the Atlantic Ocean, the Mediterranean Sea, the Adriatic Sea and off the coast of Australia. Unlike tsunamis triggered by seismic activity, meteotsunamis are driven by weather events such as fast-moving, severe thunderstorms. As scientists better understand this phenomenon and its effects, they are working to develop a reliable early warning system. In this briefing, researchers will discuss the state of meteotsunami science, the hazards they pose to coastal communities and scientists’ efforts to develop meteotsunami early warning systems in the Great Lakes and off the coastal United States.

The Great Pacific Garbage Patch — a large, floating island of plastic and debris in the eastern Pacific Ocean — appears to be growing. By sailing to the patch and measuring its accumulation over a 15-year timespan, Charles Moore from the California-based research organization Algalita has observed that the patch has swelled 27-fold by weight and 12-fold by count. Though monitoring the plastic’s impact on waters below it has proven difficult in the past, Moore plans to share details on the patch’s sprawling reach, its composition and what kind of policy changes are best in an increasingly plastic-filled world.